Safety device for electric circuits.



H. G. DORSEY.

SAFETY DEVICE FOR ELECTRIC CIRCUITS.

5 wuewtoz G ao/Pszsi Patented Jan. 14, 1919.

2 SHEETS-SHEET] $14 Gite anew APPLICATION EILED JAN.2B, l9l6- iii! H. G. DORSEY.

SAFETY DEVICE FOR ELECTRIC CIRCUITS.

APPLICATION FILED JAN.28. 191s.

Patented J an. 14, 1919.

2 SHEETSSHEEI 2 f 89 5% 3 wvewtoz HERE/SR7 C 005 57 351, 5421 61*01440135 7 To all whom it may concern:

HERBERT G. DORSEY, OF DAYTON, OHIO,

SAFETY DEVICE FOR ELECTRIC CIRCUITS.

Specification of Letters Patent.

Patented Jan. 14, 1919.

Application filed January as, 1916. Serial No. 74,853.

Be it known that 'L'HERBERT G. Donsnr, a citizen of the United States of America, and residing at Dayton, in the county of Montgomery and State of Ohio,..have invented-a certain new and Improved Safety Device for Electric Circuits, of which the following is a specification.

Myinvention relates to safety devices for electric circuits and particularly for circuits temporarily completed through an attachment plug and in which are arranged electrically operated appliances, generally of the portable type. Briefly the object of my invention is to provide means for protecting the user of such an appliance from the danger of shock occasioned by contact with a metal part of the appliance which has become accidentally charged with the power current.

Severalapplications of my invention are illustrated in the accompanying drawings,

I in which Figure 1 is a side elevation of an attach-' ment plug of ordinary screw. plug type modified in one particular 'in accordance with my invention;

Fig. 2 is a simllar view of an attachmentplug of the same type modified in a difierent manner in accordance with my invention;

Fig. 3 is an inverted plan of the latter,

Fig. 4 is a side elevation of, a plug embodying my invention and inserted in a lamp socket havinga grounded shell;

Fig. 5 is a view of a plug embodying my invention andinserted in a flush receptacle having a grounded face plate;

Fig. 6 is a more or less schematic representation of a power circuit showing different types of outlets and difierent types of I attachment plugs all embodyingmy invention'- v 7 and 8 are respectively inverted plan and side elevation of an attachment plug (or separable cap) of the blade or jack yr Fig. 9 is-a schematic side elevation of an installation in which a plug. of this typeis utilized. I V

In electrically'operated devicesof what may, 'for want of a better word, be styled the portable type, and in which the circuit is established through an attachment-plug,-

such for instance, as small motors, vibrators, cooking and laundry utensils and other domestic and thereapcutic apphances, magopposite polarity netic chucks, lamps, telephones, violet ray, X-ray, high frequency apparatus, etc., the current carrying wires or other conductors, may make accidental contact with an exposed metal part-of the appliance through a loose connection, burning out of insulation -matic means for grounding the exposed metal portions of such appliances at the moment of-the connection of the device in the power circuit.

The simplest manner of applying my invention is to supply the attachment plug of the appliance with an auxiliary contact which on the one hand is electrically connected to the exposed metal parts of the appliance, and on the other hand is adapted. on msertion in its receptacle, to make contact with a ground connection. Only attachment plugs-of standard type, modified to embody my invention, have been illustrated in the accompanying drawings.

Thus in Fig. 1 a screw plug of common construction is shown having the usual side and center contacts 10 and 11 diagrammatically connected to the wires 12 and 130i in the cable 14 through which they are led for instance to the heating coil 15 of a table cooker 16. A third wire 17 in the cable leads from a terminal 18 secured to the metallic body of the cooker to auxiliary spring terminals 19, 20, 21 and 22 on the head 23 of the attachment plug. These auxiliary terminals on the plug are so arranged that when the lug is inserted in. a suitab e receptacle there or, such as an ordinary lamp socket 24, they will make contact with the metallic'casing of the socket. Inasmuch as the latter is electrically as .well as mechanically connected through its bushing 25 with the conduit 26 and since the latter is ordinarily grounded, as diagrammatically represented 'at' 27, it is obvious that upon the insertion of the plug inthe socket,

a grounded connection from the cooker body Thus in Fig. 2, asingle'terminal 21 is shownand this is so arranged and shaped that when the plug is screwed in, the contact yields outward. This form is particularly useful in connection with flush receptacles such as shown having a cap 31 and plug jacks 32,

shown in Fig. 5. Here the auxiliary contact engages the face plate 28 which as usual is attached to the outlet box 29 into which. screws the grounded conduit 30. The ground connection is thus again automatically established upon the insertion of the plug.

In Figs. 7 and 8 a plug of another type is 33, carried thereby as usual. A third terminal3t is mounted on the plug for conned tion with the grounding Wire 35 and this terminal is connected to the spring contact 36 which, on the insertion of the plug jacks through grounded face plate 37 (Fig. 9) engages the latter and thus establishes a ground connection for the wire 35. This wire may lead for instance to the metallic casing or handle 38 of a massaging instrument or vibrator 39.

Fig. 6 is a more or less diagrammatic illustration of a system employing a polyphase alternating current generator l0. The current is led through a three phase transformer -11 to a receptacle having three terminals l2 for the power circuit and a fourth terminal 43 on ring 44: for a grounded connection 45 of any sort. The cooperating attachment plug 46 has the necessary three power circuit jacks l7 and the auxiliary terminal 48 which on the insertion of the plug, contacts with the ring at and grounds the casing t9 which is connected through wire 50 with the auxiliary terminal l8 Within the casing is a three phase induction motor 51 which operates any suitable desired utensil.

A second utensil, for instance a heater 52, is operated from the same source of power. In this case a single phase transformer 53 .is used and its secondary is grounded at 54:. The receptacle 55 is of the polarized type as is also the attachment plug 56. The metallic casing 57 of the heater is connected at 58 to the branch of the plug circuit which corresponds to the grounded side of the receptacle circuit, so that the ground connection is automatically established upon the insertion of the plug.

A third fittinghere a portable light 59, is also connected in the power-circuit. In this case the rin 60 of the receptacle 61, is grounded so that upon the insertion of the plug 62 for the lamp the aum'liary ter- 7 naenaaa minal 63 thereof connected to the lamp stand at (l-l automatically establishes the grounded connection for the stand simultaneously with the completion of the lamp circuit.

Examples embodying my invention might be endlessly multiplied with variations, but without better indicating the basic conception above described and set forth in what I claim as my invention.

I claim as my invention I 1. An attachment plug having power terminals and a grounding terminal, said grounding terminal being arranged to freely engage and ride upon the casing member of a cooperating receptacle.

2. An attachment plug having power terminals and a spring grounding terminal, said groundin terminal being arranged to have a free yielding engagement with the casing member of a cooperating receptacle, upon which casing said terminal rides.

3. An attachment plug having an insulating body provided with a gripping head, power terminals mounted on said body, and a grounding terminal mounted on the eX- terior of the head and projecting in the direction of the power terminals, but adapted to freely engage and ride upon the casing member of a cooperating receptacle.

4. An attachment plug having power terminals and a plurality of grounding terminals, said grounding terminals being arranged to freely engage and ride upon the casing member of a cooperating receptacle.

An attachment plug having power terminals and a plurality of circumferentially spaced grounding terminals, said grounding terminals being arranged to freely engage and ride upon the casing member of a cooperating receptacle.

6. In combination with a receptacle having power contacts, an insulating body and a grounded metallic casing element of an attachment plug having power terminals and a grounding contact freely engaging and riding upon the grounded casing of the receptacle substantially as described.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses.

HERBERT G. DORSEY.

Witnesses: I

II. I. "Wmson, LOUIS Pnnarrs. 

